1. Technical Field
This invention relates to hydraulic systems and more particularly to a hydraulic system particularly suitable for use on an extendable boom excavator.
2. Background Art
Material handling machinery such as hydraulic excavators of the type explained in U.S. Pat. Nos. 3,666,125 and 3,954,196 use hydraulic cylinders for raising and lowering the boom and also for extending and retracting the boom. It is desirable that the boom is not quickly lowered or extended in the event of a hose rupture. Various prior art patents such as U.S. Pat. Nos. 4,063,489 and 4,174,732 teach valves which automatically shut off fluid flow in response to pressure drop or increased flow rate which occur in the event of a line rupture.